1. Field of the Invention
The present invention relates to a nozzle presetter for a laser machining tool of a laser beam machine, capable of making adjustments outside the laser beam machine in advance so that the center of an optical axis narrowed by a machining lens will coincide with the center of a nozzle in the machining tool to be replaceably mounted on the laser beam machine, and thereby improving productivity and safety of the laser beam machine.
2. Description of the Related Art
Conventionally, a laser beam machine leads a laser beam outputted from a laser oscillator device to a machining lens, focuses it onto the focal position of the machining lens, and machining a workpiece placed near the focal position of the machining lens through instantaneous evaporation.
In addition to the laser beam, the laser beam machine needs an assist gas to hasten an oxidation reaction of the workpiece and discharge molten part of the workpiece quickly. In order for the oxidation reaction and melt discharge to proceed efficiently, the laser beam machine also needs a machining nozzle which achieves an appropriate flux diameter and flow velocity.
To carry out laser machining quickly and accurately in a stable manner using a laser machining tool (hereinafter also referred to as “machining tool”) which has the above capabilities, it is necessary to keep the nozzle accurately centered with the optical axis.
Since the machining lens is located near the workpiece, being exposed to workpiece vapor, molten particles, and other contaminants produced in its installation environment, it can always get contaminated with dirt, which lowers its transmittance, causing heat of the laser beam to build up in the machining lens. Consequently, geometry of the machining lens is changed, lowering machining accuracy and even resulting in breakage of the machining lens or otherwise disabling machining.
Thus, the machining lens is a consumable and must be changed as required.
However, the geometry of the machining lens contains a significant degree of inaccuracy for manufacturing reasons and thus, the center of the optical axis does not coincide with the nozzle center. Consequently, the nozzle must be centered with the optical axis each time the machining lens is changed.
To center the nozzle with the optical axis, machining is stopped with a machining tool mounted on the laser beam machine, a target is attached to a nozzle tip, a low-power laser beam is emitted from a laser oscillator device for a short time, the machining nozzle is moved horizontally by manually turning adjustment screws of the nozzle with reference to a burn mark left on the target by the beam, making the nozzle center to coincide with the burn mark.
Also, there is a known centering method which involves mounting a bending mirror on a mirror holder capable of angular adjustments to center the nozzle with the optical axis (see Japanese Patent Laid-Open No. Publication 2003-170287 (Patent Document 1)).
Besides, there is a known centering method in which an optical flat capable of angular adjustments is mounted above a condenser lens, a mirror reflector for use to observe a jet orifice for assist gas and machined hole in the workpiece is mounted below the condenser lens, and the nozzle is centered with the optical axis using the optical flat based on images picked up by a CCD camera via the mirror reflector (see Japanese Patent Laid-Open Publication No. 2003-225287 (Patent Document 2)).
Since the operation of centering the nozzle with the optical axis must be performed on the machine, machining must be stopped temporarily, resulting in reduced productivity. Besides, it requires skill to center the nozzle sufficiently with the burn mark left on the target.
It is not possible to predict when a machining lens needs replacement due to its failure. Besides, such replacement must always be carried out manually. This makes it impossible to accomplish long, unattended operation.
The laser beam directed at the target is a powerful one outputted from a laser oscillator device for machining. Thus, an operation which requires the operator to bring his/her eyes close to the nozzle involves danger.